1. Field of the Invention
This invention relates to a method and apparatus for hydraulically transferring coal in log or capsulized form, through a pipeline.
2. Description of the Prior Art
Processes for transferring coal in an aqueous slurry over long distances through pipelines have been in use for many years. One such process is set forth in U.S. Pat. No. 2,791,471. The '471 patent provides for a coal slurry transfer in batches, which batches are spaced apart by lower density fluid carriers, such as water. The batches are spaced apart because the quantity of coal which is transported through a pipeline generally is not sufficient to keep the pipeline full of coal slurry at all times. However, transporting coal in batches spaced apart by water resulted in plugging due to the inability of the low density water, acting as a hydraulic transportation media, to maintain in suspension heavier coal particles present in the slurry.
The plugging difficulties were lessened by use of principles such as those disclosed in the U.S. Pat. No. 2,920,923. A slug of liquid material was provided in the pipeline in advance of and following the main slurry slug. The slug of liquid material came to be known as a "pseudo fluid" and differed in composition and density from both the main slurry slug and the water carrier component of the slurry. In particular, the pseudo fluid density was less than that of the main slurry slug but greater than that of the water carrier. Because a fluid carrier's ability to maintain heavier coal particles in suspension is directly proportional to its fluid density, the pseudo fluid (having a density greater than that of the water carrier) was found to be an effective means to maintain the larger coal particles in suspension and, thus, reduce plugging in the pipelines. Use of the pseudo fluid in front of and behind of the main slurry slug provided a more dynamically stable slurry in the pipeline.
However, creation of the pseudo fluid having the desired properties involved a costly process of fabricating a range of coal particles with certain size distribution, for mixing with water. Further, since effective and economic use of such pseudo fluids required their re-use with numerous main slurry slugs, special handling systems were required, including storage facilities and associated pumps and piping to store the pseudo fluid when not in use. Further, pseudo fluids were not 100% effective at maintaining larger coal particles in suspension and, thus, the plugging problem was not totally resolved.
Other problems arose where a single pipeline furnished coal in batches to several plants along the pipeline. In order to provide a portion of the coal slurry to a particular plant, it was often necessary to remove all of the coal slurry from the pipeline to stablilize pipeline operations and to balance different flow rates in each section of the pipeline. Such a process called for the reformation of the pseudo fluid in front of and behind each batch (called the cap and tail, respectively) whenever the remaining coal slurry batches were returned to the pipeline for movement to the next downstream delivery point. The requirements of reforming the cap and tail increased the cost of the commercial coal slurry pipeline process.
Other disadvantages associated with commercial coal slurry pipeline processes include high costs associated with: (1) pulverization of coal necessary for slurry operation; (2) high liquid carrier to coal mass ratio for effective transfer; and (3) coal dewatering and drying processes required prior to use of coal after transfer. Further, coal slurries do not readily restart after stopping the carrier motion because after larger coal particles settle out of the liquid carrier and come to rest on the pipe floor under static conditions, they are not readily returned into suspension in the restarted carrier from their resting position. Finally, coal slurries are highly abrasive to pipelines, especially in pipeline bends.
Other procedures have heretofore been proposed for transporting materials, such as coal, through pipelines which are improvements over the disadvantages referenced above. Such procedures have included material transfer by use of rigid-walled containers into which are inserted materials to be transported. The containers are hydraulically moved through the pipeline. Such procedures, however, suffer many disadvantages including those associated with container manufacturing costs and difficulties associated with container handling. Disclosed in the Hodgson et al. U.S. Pat. No. 3,333,901 is a method and apparatus which sought to overcome these difficulties by providing a process for the fabrication of the substances to be transported into coherent shapes, bodies or packages prior to insertion in the pipeline. While the Hodgson '901 reference states that each particular material may be packaged in a manner best suited for the most efficient transportation thereof, and offers some guidance regarding ranges of the ratio of package density to the density of the fluid carrier (e.g. (10.0-1.0) to (7-1)), the '901 reference does not teach nor suggest the dynamic operating parameters necessary for the cost effective operation of a pipeline carrying coal capsules having a cylindrical shape. The method disclosed in the '901 reference for transporting coal shaped into cylindrical packages could cause excessive energy consumption and damage both the coal package and the interior surfaces of the pipeline.
Heretofore, there has not been available a coal pipeline material transport process or apparatus with the advantages and features of the present invention.